1. Field of the Invention
The present invention relates to a disk cartridge for rotatably containing a disklike medium such as an optical disk, a magnetic optical disk and the like.
2. Description of the Related Art
Disk media such as heretofore known optical disks, magnetic optical disks and the like may be classified according to disk diameter as follows: magnetic disks of 5 inch and 3.5 inch or optical disks of 6.5 cm (MD), 8 cm (CD single), 12 cm and the like.
Of these disks, the 12-cm CD and the 8-cm CD are not different in adopting the same data storage system but only diameter. Although playback machines were initially designed to replay the 12-cm CD in a standard mode and also the 8-cm CD by additionally fitting an adaptor thereto, those machines of today are usable for replaying both the 8-cm and 12-cm CDs.
On the other hand, disk cartridges for rotatably holding a disklike medium are well known. A disk cartridge of this sort generally consists of an upper and a lower case, and slidable shutters. Each of the upper and the lower cases is formed with an opening into which a record-playback head, for example, is inserted. The slidable shutters are U-shaped in cross section and used for exposing and blocking up the respective openings.
With respect to such an optical disk of 12 cm in diameter, though what is mounted nakedly in a playback machine like a CD is already known, a DVD-RAM containing an optical disk of 12 cm in diameter in the case has recently been proposed.
When the optical disk of 12 cm in diameter (hereinafter called the "12-cm disk cartridge") is held in the case, the opening of the case is required to have a width of about 4 cm if the size of the record-playback head on the machine side is taken into consideration. Furthermore, the width of the shutter needs to be greater than at least the width of the opening of the case. When the opening is left exposed, the shutter must not be positioned above the opening. Even if the opening of 4 cm in width is formed in the 12-cm disk cartridge, a space of greater than 4 cm in width can be secured on both lateral sides of the 12-cm disk cartridge. Therefore, shutter-retracting spaces for causing the opening to be left exposed can be provided.
When the optical disk of 8 cm in diameter (hereinafter called the "8-cm disk cartridge") is held in the case, in order for the 8-cm disk cartridge to be made usable by a record-playback machine intended for the 12-cm disk cartridge, the record-playback head for the record-playback machine has to be formed so that it can be passed through the opening. In other words, an opening of 4 cm in width must be formed even in the 8-cm disk cartridge.
As the external size of the disk cartridge is desired to be smaller, it is ideal to set the breadth of the 8-cm disk cartridge at about 9 cm. However, only a space of about 2.5 cm can be secured on both sides when an opening of 4 cm in width is formed at, for example, 9 cm in breadth. This means a shutter of not less than at least 4 cm in width is needed to cover the opening of 4 cm in width and the problem is that a shutter-retracting space for use in keeping the opening exposed becomes impossible to provide.
In order to solve the above problem, it is reasoned to provide bisected double shutters as disclosed in, for example, Examined Japanese Patent Publication No. Hei 5-4752. As described in this publication, however, there develop problems arising from an increase in the number of parts and raising production cost because two pieces of guide bars have to be provided and because a spring has to be provided to each shutter. Moreover, a spring and the like in both corner portions should be arranged inside a disk cartridge arises. Accordingly, it is difficult to reduce the size of the disk cartridge. There still exists a problem in that the merit of compactness that the single-sided CD has cannot be brought out.
Most of the above-described disk cartridges have the mechanism of using only one side and as an error insertion preventive mechanism. There has been employed a method for preventing error insertion by making different the configuration of one end portion on the insertion side of such a disk cartridge. By adopting this shape, it is possible to prevent the disk cartridge from being inserted upside down by mistake and also from being inserted reversely (Examined Japanese Patent Publication No. Hei 7-66618).
If the upper and lower configurations of a conventional disklike medium capable of record-playback on both sides are set similar to each other so that a disk cartridge may be inserted upside down, the conventional mechanism of preventing the disk cartridge from being inserted reversely by mistake fails to function as what prevent such error insertion. In consequence, a groove B' is provided on both side faces close to the insertion side of a case A' as shown in FIG. 18 in order to detect the error insertion by causing the error insertion detecting member C' of a record-playback machine to engage with the groove B'.
In the case of such a detection structure, the joint between the stationary side and movable side of a mold for molding cases, for example, a parting line (hereinafter simply called the PL plane) varies. Accordingly, this not only makes the mold structure complicated but also necessitates an extra member for the error inserting preventive mechanism on the record-playback machine side. Therefore, there arises a problem of high cost.